1. Field of the Invention
is invention relates to an atrial defibrillator apparatus and a method for automatic intravenous delivery of a defibrillating drug into the bloodstream of a patient in need of atrial defibrillation.
2. Description of Related Art
Atrial fibrillation (AF) is the cardiac arrhythmia that seems to occur most frequently. Although it is not usually life threatening, cardiac arrhythmia is associated with strokes apparently caused by blood clots that form after prolonged AF. The onset of AF is often unexpected and occurs suddenly. Drugs are currently available for atrial defibrillation by intravenous infusion. However, intravenous delivery often requires specialized skills of medical personnel at relatively remote facilities. AF can also be treated with a discharge of electrical energy to the heart, through the skin of the patient, by way of an external defibrillator of the type well known to those skilled in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the chest in synchronism with a detected ventricular electrical activation (R wave) of the heart. Such treatment is very painful and requires skills and special facilities found only in treatment centers such as hospitals.
Certain disadvantages associated with conventional implantable electrical atrial defibrillators have prevented mass production and common use as means for treating AF. U.S. Pat. No. 5,265,600 teaches a device that delivers defibrillating electrical energy to the atria via intracardiac electrodes. As with many other conventional defibrillators, such energy often results in the patient experiencing severe pain. Such energy may also induce ventricular fibrillation, which can be a fatal cardiac arrhythmia.
It is known that after successful defibrillation of the atria, the atria of the heart typically beat at a low rate, particularly if there is temporary sinoatrial node dysfunction resulting from the defibrillation of the atria. The sudden reduction in cardiac rate could potentially result in the patient experiencing a spell of dizziness. In addition, the sudden reduction in cardiac rate can also lead to dispersion of refractoriness which, if it occurs together with an R on T condition, can render the heart more vulnerable to ventricular fibrillation. Hence, such a sudden reduction in cardiac rate following successful defibrillation of the atria may be quite undesirable.
The implantable atrial defibrillation apparatus and method of this invention overcomes the disadvantages associated with conventional electrical atrial defibrillation apparatuses by using pharmacologic atrial defibrillation instead. This invention also overcomes the problem of low heart rates normally encountered after defibrillation, by automatically pacing the atrium, if required. Another advantage of this invention is that it automatically provides this same type of pacing, known in the art as the AAI mode, under circumstances such as sinus node dysfunction, and thus can aid in preventing atrial fibrillation in some patients.